There is a variety of applications for measuring a surface contour of three-dimensional bodies, for example in digitizing spaces, as employed for issues relating to statics in civil engineering or for multimedia applications, or in quantitative quality control, in particular in industrial production. In this case, the high-precision measurement of very large objects having a characteristic dimension of a few meters with a resolution in the micrometer range represents a challenge.
For the measurement of object surfaces with the aid of optical-geometrical techniques, such as the fringe projection and deflectometry, there is an interconnection between lateral resolution and depth of field. This has the effect that optimizing one variable gives rise to a worsening of the respectively other one, and that it is thus difficult to attain lateral accuracies in the micrometer range over depths of fields of a few meters.
Tactile coordinate measuring machines attain high precisions in volumes of a few cubic meters. These measurements can, however, be time-consuming, in particular when positions of a large number of points distributed over the surface of the measurement body are to be determined. Coordinate measuring machines for objects having characteristic dimensions in the range of meters are massive, non-mobile apparatuses. Moreover, the use of a tactile measurement has no, or only limited, applicability to sensitive surfaces.
Laser path length measuring devices allow the distance of an object to be determined. In K. Minoshima and H. Matsumoto, “High-accuracy measurement of 240-m distance in an optical tunnel by use of a compact femtosecond laser”, Applied Optics, Vol. 39, No. 30, pp. 5512-5517 (2000), a distance measurement using frequency combs under laboratory conditions is described. While the measurement can be made with a high precision, it is limited to one dimension and requires light reflection on the object.
EP 1 903 302 A2 describes an optical device which combines a sinusoidal amplitude modulation with a pulsed light output of a light source in order to determine a distance of an object. In DE 11 2005 001 980 T5, a method and a device are described in which frequency comb light is coupled into an optical interferometer to perform a distance measurement. An observation depth in the object is controlled by closed-loop control of a modulation signal. The surface of an object can neither be measured with the method of EP 1 903 302 A2 nor with the method of DE 11 2005 001 980 T5.